Effective periods and dampings of building-foundation systems including seismic wave effects

Effective periods and dampings of a refined soil-structure system similar to that used in practice to account for the inertial interaction effects are determined, including the kinematic interaction effects for the important special case of vertically incident shear waves. A three-dimensional axisymmetrical model consisting of a single structure with embedded foundation in a soil layer over elastic bedrock is examined. The impedance functions and the input motions for the foundation are computed respectively by an efficient numerical technique and the well-known Iguchi averaging method. Effective periods and dampings are determined for a large number of system configurations. Results are presented by means of dimensionless charts that should be used by designers in code-analyses of soil-structure interaction. Diagrams should also be of use in preliminary analyses to assess the influences of the principal parameters involved. Moreover, accurate approximate formulas for the effective period and damping are proposed, the use of which is very simple.